Heat pump design, installation and commissioning - step by step
- Mario Dodić
- Jan 14
- 5 min read
Updated: Jan 17
This heat pump system in the HVAC Education Hub training centre in Zagreb was designed, installed, and commissioned by me, without previous hands‑on heat pump installation experience.
My father-in-law, who is a construction engineer, helped with installation.
The goal was simple: follow physics, manufacturers’ instructions, and best practice to prove that with the right education, anyone can deliver an efficient, comfortable, and stable system
(P.S. I have many years of experience in heat pump design, commissioning, troubleshooting, and training, but with zero installation experience).
Here is a link for Open Energy Monitor, where live data from the system is shown:
Design
The building is an older house with poor building fabric and many construction defects, now used as an office and training space:
Total area: 40 m² (office/training 30 m², kitchen 5 m², bathroom 5 m²)
Blower door test: around 15 ACH at 50 Pa, which equates to roughly 4 ACH in real conditions, so realistic design infiltration had to be adjusted room by room. I put 1.5 ACH in every room as defects will be gradually fixed
NOTE: Ventilation heat loss is one of the “guesswork” in our industry, and we covered that topic in video.
And in the article.
Insulation: 5 cm EPS on most external walls and 20 cm loft insulation over roughly half of the office; mixed PVC and timber windows. Floor is uninsulated.
With all this, calculated design heat loss at the 99% winter condition for Zagreb (−6.7 °C) was 3.54 kW.
NOTE: Check this video where is explanation why design for the coldest day is not always the best idea.
Existing radiators in the office and bathroom stayed, while the kitchen emitter was upsized and an additional radiator was added in the office to support lower flow temperatures. All of them K2, with a bathroom towel rail.
Key design decisions:
Design flow temperature: 50 °C on -6.7 °C, mainly driven by the bathroom and kitchen as the coldest rooms, with the expectation that the real operating temperature will often be lower because this is not a full‑time living space
Pipework inside the office without insulation, so distribution losses also help space heating instead of being wasted
This is exactly the type of “imperfect” real‑world - not a showroom house, but typical existing housing where good design still makes the system work.
Installation
The chosen unit is a Bosch Compress 5800i monoblock (R290), a robust 180 kg outdoor unit with an indoor unit (integrated pump, backup heater, and three‑way valve for heating/DHW in the indoor module).
Copper pipework is 22 mm between the heat pump, indoor unit, and main distribution, with existing 18 mm and 15 mm branches retained at the radiators where capacity allowed.
Hydraulic and training features installed
5 radiators, all with flow regulating valves for proper balancing instead of simple lockshields
50 L volumiser on the return to increase system volume and support stable modulation
200 L DHW tank with 2.6 m² coil plus separate expansion vessel for domestic hot water
Dedicated expansion vessel for heating circuit
Low loss header, secondary pump, and two ESBE VRG valves to allow:
Open‑loop / direct connection
Separation via low-loss header (LLH)
Different training and test configurations with or without a secondary pump.
Deaerator, magnetic filter, flow and balancing meter, antifreeze valves, and full valve isolation on all key components
Heat Pump Monitor and electricity meters for real‑time performance tracking and transparent data
All press joints are Viega, with leaks limited to threaded connections on components – and even those were easy to fix because every component was designed with isolation in mind.
This is a key learning point: good design plus correct sequence of valves and fittings makes troubleshooting simple, even for a non‑plumber.
On the electrical side, outdoor unit, indoor unit, secondary pump, ESBE valves, and monitoring all have separate protection and clear wiring.
Commissioning
Commissioning is often the most underrated step in the whole process, but it has the biggest impact on efficiency, comfort and running cost.
Because this office is not occupied 24/7, the target schedule is 21 °C during working hours (Monday–Friday, 8:00–16:00) with setback to 18 °C at other times.
Three core commissioning lessons from this installation:
1. Know the controller in detail
Each manufacturer has different logic, menus, and parameters.
Time invested in understanding the software (weather compensation, room influence, pump control, DHW logic, alarms) is returned many times over in stability and performance.
2. Modulation is king
Long, slow, continuous operation at the lowest possible flow temperature delivers:
Lower electricity consumption.
Higher efficiency (COP/SCOP).
Longer component life.
With good water volume and correct weather compensation, this system could run radiators at 33 °C when the outdoor temperature was around 0 °C – lower than the original design assumption. Here is data with COP 4.72:
What is also important with low and slow heating is that defrost cycles are very rare. Here is one example of defrost. In 1-2 minutes, the ice is melted, and the unit is in normal heating mode again:
And here is example with -14.5°C outdoor temperature, much lower than designed and still indoor temperature is 22 °C with COP=2.9 in 24 hours below 0 °C and the coldest day in last 12 years in Zagreb:
3. Balancing is mandatory
Every radiator was balanced so each room gets exactly the heat output expected from the design.
In most systems seen in the field, this simple but vital step is skipped, and then installers blame the heat pump instead of the hydraulic setup. Here is one radiator captured with thermal camera. Constant temperature across radiator:
One example of software impact:
Factory room influence was left too high – it means, flow temperature is going up
When indoor temperature was below setpoint, the controller started to override weather compensation, driving flow temperature from 32 °C up to 42 °C
Result: electrical power jumped from about 500 W to around 1.6 kW – more than a 300% increase :
After reducing room influence, consumption dropped back to expected levels and the system “locked in” to stable modulation
This is exactly the type of subtle but critical behaviour that needs to be understood if installers want truly efficient systems – and it is hard to learn from manuals alone.
Conclusion
This whole installation was created as a live teaching tool for Heat Pump Journey, the new online heat pump education platform of HVAC Education Hub.
The platform is built around five structured courses:
1. Introduction & Technology
2. Design
3. Installation
4. Control Strategy & Commissioning
5. After Sales, Maintenance & Service
Each course is broken down into microlearning modules with short videos, animations, drawings, and interactive assessments so learners can move from theory to practice step by step, with science of learning in mind. For example, Four way valve microlearning:
1. Short text
2. Video
3. Interactive visual assessment
This real installation in Zagreb is used throughout the platform as a case study, showing how design, installation, and commissioning decisions translate into real performance – and proving that with the right learning approach, you can do the same on your projects.
If you want to be notified about the launch and get access to over 100 lessons focused on real‑world heat pump practice, you can find more details here.
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